Congenital deafness with labyrinthine aplasia, microtia, and microdontia, also known as LAMM syndrome is a health condition that affects development of the ears and teeth. In people with this condition, the structures that form the inner ear are usually completely absent (labyrinthine aplasia). Uncommonly, affected individuals have some underdeveloped inner ear structures in one or both ears. The irregularities of the inner ear cause a form of hearing loss called sensor-neural deafness that is present from birth (congenital). Because the inner ear is important for balance as well as hearing, development of motor skills, such as sitting and crawling, may be delayed in affected infants. In addition, people with LAMM syndrome often have peculiarly small outer ears (microtia) with narrow ear canals. They can also have unusually small, widely spaced teeth (microdontia).

Is congenital deafness with labyrinthine aplasia, microtia and microdontia common?

Congenital deafness with labyrinthine aplasia, microtia and microdontia is a rare health condition, although its occurrence is unidentified. At present, a dozen affected families have been identified.

Which genes are linked to congenital deafness with labyrinthine aplasia, microtia and microdontia?
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LAMM syndrome is caused by mutations in the FGF3 gene, which provides instructions for making a protein called fibroblast growth factor 3 (FGF3). By attaching to another protein known as a receptor, the FGF3 protein triggers a series of chemical reactions inside the cell that signal the cell to undergo certain changes, such as dividing or maturing to take on specialized functions. During development before birth, the signals triggered by the FGF3 protein stimulate cells to form the structures that make up the inner ears. The FGF3 protein is also involved in the development of many other organs and structures, including the outer ears and teeth.

FGF3 gene mutations involved in LAMM syndrome alter the FGF3 protein. The changed protein likely has reduced or absent function and is unable to stimulate signalling. The loss of FGF3 function affects development of the ears and teeth, which leads to the features of congenital deafness with labyrinthine aplasia, microtia and microdontia.

How do individuals get congenital deafness with labyrinthine aplasia, microtia and microdontia?

Congenital deafness with labyrinthine aplasia, microtia and microdontia is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.